A mobile phone network conventionally consists of a plurality of base stations arranged in a pattern so as to define a plurality of overlapping cells which provide radiocommunication support in a geographic area. Base stations are located so as to provide optimal coverage of the mobile phone service area. As shown in FIG. 1, the transmission pattern of a geographic arrangement of network base stations typically looks like a honeycomb of cells. Each base station in the network serves a roughly circular area with a diameter ranging from a few hundred meters to several kilometers depending on population density. The mobile phone network typically only has a specified number of frequencies available for use by mobile subscribers. Therefore, to maximize use of the specified number of frequencies while preventing interference between adjacent base stations, each base station supports different frequencies than its corresponding adjacent base stations. When a mobile subscriber moves to the edge of a cell associated with a current servicing base station the mobile subscriber can be "handed-off" to an adjacent base station so as to enable call quality and signal strength to be maintained at a predetermined level.
Occasionally, areas of inadequate network coverage exist within a cell, or between cells, that cannot be circumvented by "hand-off" to a neighboring cell. Examples of such areas (17, 18, 19) are shown in FIG. 1 and typically occur due to geographical terrain, large buildings, or poor cell tuning, for example. These areas of inadequate network coverage can impair the quality of the mobile subscriber signal, and also impair the ability of the network to avoid call dropping. In areas where the transmission level is weak, the quality of the phone signal will likely be degraded. Furthermore, in geographic areas of very poor network coverage, the potential for call dropping exists.
Conventionally, adequate network coverage is monitored through the performance of drive tests by network operator staff. To perform this monitoring, operator staff drive throughout the network and conduct and record call quality checks. A conventional system such as TEMS (Test Mobile System) is used to perform the monitoring. TEMS uses mobiles modified with specialized software for monitoring parameters of the radio environment. Radio environment monitoring is initiated by an operator who connects the modified mobile to a personal computer via a standard RS-232 serial connection. A GPS receiver is also connected to the PC to provide mobile position information. Survey data is then compiled during the monitoring process including data such as the geographic locations associated with signal strengths, bit error rates, interference, or dropped calls. Post-processing of the data gathered by TEMS is performed in a geographical information system (GIS) that enables the operator to visualize survey data with different colors and symbols that are indicative of status and operation of the mobile.
The conventional monitoring technique exemplified by TEMS, however, requires an inordinate amount of resources to survey the network. Such resources include extra monitoring equipment, extra staff to conduct the drive tests, and additional staff time to drive around and survey the network. Furthermore, the time delay between the actual time at which an inadequacy in network coverage begins to exist and the time taken to survey the network, tabulate the results, and implement changes in the network coverage, ensures a period of degraded performance to affected mobile subscribers.
Accordingly, it would be desirable to provide a technique for monitoring a cellular network that minimizes the time required to detect areas of poor network coverage and which further minimizes the necessity of operator intervention.